In recent years, gallium nitride compound semiconductors represented by the formula AlxInyGa1-x-yN (0≦x<1, 0≦y<1, x+y<1) have become of interest as materials for producing a light-emitting diode (LED) which emits ultraviolet to blue light, or green light. Through employment of such a compound semiconductor, ultraviolet light, blue light, or green light of high emission intensity can be obtained; such high-intensity light has conventionally been difficult to attain. Unlike the case of a GaAs light-emitting device, such a gallium nitride compound semiconductor is generally grown on a sapphire substrate (i.e., an insulating substrate); hence, an electrode cannot be provided on the back surface of the substrate. Therefore, both a negative electrode and a positive electrode must be provided on semiconductor layers formed through crystal growth on the substrate.
In the case of the gallium nitride compound semiconductor device, the sapphire substrate is transparent with respect to emitted light. Therefore, attention has been paid to a flip-chip-type light-emitting device, which is configured by mounting the semiconductor device on a lead frame such that the electrodes face the lead frame, whereby emitted light is extracted through the sapphire substrate.
FIG. 1 is a schematic representation showing a general structure of a flip-chip-type light-emitting device. Specifically, the light-emitting device includes a substrate 1, a buffer layer 2, an n-type semiconductor layer 3, a light-emitting layer 4, and a p-type semiconductor layer 5, the layers being formed atop the substrate through crystal growth. A portion of the light-emitting layer 4 and a portion of the p-type semiconductor layer 5 are removed through etching, thereby exposing a portion of the n-type semiconductor layer 3 to the outside. A positive electrode 10 is formed on the p-type semiconductor layer 5, and a negative electrode 20 is formed on the exposed portion of the n-type semiconductor layer 3. The light-emitting device is mounted on, for example, a lead frame such that the electrodes face the frame, followed by bonding.
During mounting of a flip-chip-type light-emitting device, the device is heated to some hundreds of degrees Celsius. Therefore, the flip-chip-type light-emitting device is required to resist deterioration in characteristics and exhibit consistent characteristics at a temperature of some hundreds of degrees Celsius.
In the gallium nitride compound semiconductor light-emitting device, a portion of a gallium nitride compound semiconductor layer must be removed through etching for forming the aforementioned negative electrode. Reactive ion etching employing reactive gaseous plasma is a known technique for etching gallium nitride compound semiconductors, and has conventionally reported in a number of documents.
A large variety of etching gases such as Cl2, a Cl2/H2 mixture gas, CF4, CCl2F2, CCl4, BCl3, a BCl3/Ar mixture gas, a BCl3/SiCl4 mixture gas, SiCl4, and an SiCl4/SiF4 mixture gas have been studied in terms of etching rate, etching residues produced, and other characteristics. Japanese Patent No. 2599250 and Japanese Laid-Open Patent Application (kokai) No. 8-293489 disclose that a Cl2/SiCl4 mixture gas is preferred from the viewpoint of etching rate and etching residue characteristics.
However, these etching gases have not been studied from the viewpoint of reliability in characteristics of the produced gallium nitride compound semiconductor light-emitting devices under high-temperature conditions.